The accused allegedly conspired to buy hundreds of machine-guns, rockets and explosives from US federal agents who were working undercover as arms dealers.

They are said to have sought to spend millions of dollars on weapons to carry out attacks.

Prosecutors said the coup leaders planned to blow up government buildings and kill "thousands of people".

The "Hmong insurgency planned to use AK-47 automatic rifles, Stinger missiles, LAW rockets, anti-tank rockets and other arms and munitions to topple [the] Lao government and reduce government buildings in Vientiane to rubble," a public prosecutor in California said in a statement.

Laos Foreign Ministry spokesman Yong Chanhthalansy said it was "great news" for Laos.

"We hope the United States will prosecute them strictly under the Patriot Act and punish the violators of the law severely," he told the Reuters news agency.

Mr Yong said he hoped the development would improve relations with neighbouring Thailand, whom Vientiane has suspected of turning a blind eye to Hmong militant activity within its borders.

"I am sure that such vigorous investigation will lead to the uprooting of the network of the villains who have caused the most difficulty in bilateral relations between the Lao and Thai governments," he said.